Time delay undervoltage protective system



' May 14, 1935.

B. W. JONES TIME DELAY UNDERVOLTAGE PROTECTIVE SYSTEM Filed Oct. 19, 1935 Inventor: BenJam in WJones,

H is Av Lorneg.

Patented May 14, 1935 UNITED STATES PATENT OFFICE Benjamin W. Jones, Schenectady, N. Y., assignor to General New York Application October 19,

13Clalma.

My invention relates to the provision of a control system which will aiiord time delay protection in the event of a dip in the line voltage, and has for an object the provision of a simple, reltiable and inexpensive system of this charac er.

Heretofore no-voltage protective devices have been provided in systems so that translating devices are deenergized in the event the line voltage decreases a predetermined amount'or suddenly drops to zero. It has been recognized that such protective devices should not deenergize the translating devices, for example driving motors and the like, upon a momentary dip in the line voltage since the translating devices are not inlured by a momentary reduction in voltage. Accordingly, it has been proposed to delay the action of the no-voltage protective device by means of various forms of mechanical timing devices. Much is yet to be desired, however, in providing a timing device for the undervoltage protective system wherein the moving parts of mechanical timing devices are entirely'eliminated.

In carrying out my invention in one form thereof I provide time delay undervoltage protection by taking advantage oi the time interval required for the decay of the fiux in a substantially closed magnetic circuit. More specifically, I provide a direct current relay with a substan tial amount of magnetizable material for the substantially closed magnetic circuit and I connect the relay operating coil in series circuit relation with a rectifier across an alternating current supply circuit, a normally closed circuit also being provided for the operating coil. The circuit of the relay coil is also connected in series with interlock contacts operated by a load-controlling contactor. As long as the voltage of the alternating current is approximately normal, the contactor is maintained in closed circuit position. As soon as the line voltage decreases a predetermined amount, for example per cent of normal voltage, the contactor is operated to its open circuit position, its interlock contacts serving to disconnect the relay coil from the sup'-' ply source. The magnetic flux of the relay immediately begins to decay, an-interval of from one to ten seconds being required before the corresponding reduction in the attractive eifort of the relay permits it to open the energizing circuit of the contactor. If during this time interval the line voltage should increase above the pick-up value of the contactor, for example 50 per cent of normal voltage, the contactor would close and the relay would again be energized Electric Company, a corporation of 1983, Serial No. 894,275

preparatory for the next timing operation. I further provide means for permitting at any time instant operation of the armature from its attracted to its unattracted position.

For a more complete understanding of my invention "reference should now' be had to the accompanying drawing wherein I have shown diagrammatically in Fig. 1 one form of my invention, Figs. 2, 3 and 4 illustrating diagrammatically additional modifications of my invention.

Referring to the drawing, I have shown my invention in one form as applied to an alternating current supply circuit, represented by the conductors l0 and II, arranged to supply a load or translating devicel2 whenever a contactor II is operated to its closed circuit position. The energization oi the contactor i4 is controlled by means of 'a push button It and an undervoltage protective relay il provided with a substantially closed magnetic circuit I8 and a magnetizable armature it. The operating coil 20 of the relay is connected across the midpoints 2| and 22 of a full wave rectifier 23, the rectifier being connected from opposite mid-points 24 and II, respectively, by conductor 24a to the supply line Ill and by interlock contacts 26 of the contactor It to the other supply line H. A normally closed push button 28 is connected in series circuit relation with the operating coil 20 of the relay ll. The magnetizable material included in the magnetic circuit of the undervoltage relay I1 is considerably greater than the amount required to operate the armature I! from its un-, attracted position to its attracted position against the bias of the spring 29. Consequently, by maintaining a closed circuit for the operating coil 20 the decay of flux in the relay I I occurs quite slowly and I have found that in practice a delay of from one to ten seconds can be obtained solely by reason of the magnetic energy stored in the magnetic circuit.

In order to close the contactor H the normally open push button It is operated to complete a circuit for the operating coil of the contacts which extends from supply line it by conductor 30, the contac'ts'of the push button It, conductor 3 i, operating coil of the contactor l4 and by conductor 32 to the other supply line H. Consequent to the closing 01 the contactor M an energizing circuit for the operating coil 20 of the undervoltage relay I! is completed through the interlock contacts 26, the full wave rectifier 23 transforming the alternating current into direct current. The armature I8 is thereupon operated to its attracted position to close its contacts and thereby complete a holding circuit for the operating coil of the contactor M.

It will now be assumed that a voltage dip occurs, for example a reduction in voltage of 50 per cent normal voltage, in the alternating current supply lines it and ii, and that this reduction in voltage is suilicient to permit the opening of the-contactor l4 and its interlock contacts 26. The relay i! will, therefore, be deenergized and it will be apparent that the flux in the magnetic circuit it of the relay {1 will begin to decay. The rate of decay, however, will be relatively slow inasmuch as the relay coil remains connected in a closed electrical circuit to permit a fiow of current and the production of a magnetomotive force tending to maintain the attractive effort of the relay. This circuit may be. traced from one side of the coil 20, through normally closed push button 28, through the rectifier 23 and to the other side of the coil 20. i I have found that a time delay of from one to ten seconds can be obtained before the relay is operated to its open circuit position. If, however, the line voltage increases during this time interval to a value above the pick-up value of the contactor I4, for example 80 per cent normal voltage, the contactor will be operated to its closed circuit position whilst the relay I! will again be energized through the interlock contacts 26 and the rectifier 23. II the relay operates to its open circuit position, however, the holding circuit for the contactor is interrupted. It is, therefore, necessary to operate the normally open push button Hi to close the I contactor |4.

If at any time it is desired to deenergize the contactor l4 it is only necessary to operate the normally closed push button 28 to its open circuit position thereby interrupting the energizing circuit for the relay coil 20. In this case it will be observed that the undervoltage relay immediately interrupts the holding circuit because the decay of the flux occurs very quickly when the coil 20 is open circuited.

Referring now to Fig. 2, I have shown the relay ll of Fig. 1 energized by a half wave rectifier 34 instead of the full wave rectifier 23. In this form of my invention a second rectifier 35 is connected in shunt with the coil 20 so as to permit circulating current to flow after the interlock contacts 26 have opened but prevents the flow of current from supply line l0 through this shunt circuit and to the other supply line H during normal operation. The normally closed push button 28 serves to deenergize the coil 20 and to interrupt the shunt circuit through the rectifier 35 for instantaneous opening of the contactor l4.

In the form of my invention shown in Fig. 3 it will be observed that the undervoltage relay I1 is provided with a closing coil and a diflerential coil 4| and that a half wave rectifier 42 is connected in circuit with the relay coils. The contactor l4 in this case is provided with a pair of interlock contacts 44 and 45. In order to close the contactor a normally open push button 46 completes an energizing circuit for the relay I! which may be traced from the supply line III by conductor 41, interlock contacts 44, conductor 48, push button 46, normally closed push button 49,

. conductor 50, coil 4| of relay I I, conductor .i2, rectifier 42, and by conductor 53 to the other supply line H. The closing coil 4| thereupon operates the relay IT to the closed circuit position to complete an energizing circuit for the operating coil or the contactor l4. ,This circuit may be traced from the supply line III, by conductor 55. operating coil of the contactor, conductor 58, contacts of relay l1, and by conductor 5! to the other supply line H. Consequent to the closing of the contactor M an energizing circuit is completed for the load l2 whilst the normally closed interlock contacts 44 remove a short circuit around a holding resistor 58, which resistor serves to reduce the current flowing to the relay coil 4|. At the same time the interlock contacts are closed to complete a holding circuit for the relay I! which circuit may be traced from the supply line I0, conductor 41, holding resistor 58, conductors 48 and G0, interlock contacts 45, conductors 6| and 62, normally closed push button 49, conductor 50, operating coil 4|, conductor 52, rectifier 42, and by conductor 53 to the other supply line II.

It will now be assumed that a voltage dip occurs on the supply lines I0 and ll of sufficient magnitude to permit the contactor l4 to open. The interlock contacts 44 and 45 interrupt the holding circuit of the relay l1 and the magnetic flux of the relay I'I begins to decay. The change in the flux conditions or the magnet l1 gencrates current in the coil 40 of the relay, which current fiows in a normally closed circuit which may be traced from one side of the coil 40, by conductors 6| and 82, normally closed push button 49, and by conductor to the other side of the coil. This current flowing through the coil 40 produces a magnetomotive force which tends to maintain the flux in the relay H. The relay H is, therefore, maintained in its closed position against the bias of the opening spring 29 until the attractive effort produced by the magnetic flux decreases to an amount less than the force supplied by the opening spring 25. By adjusting the spring 29 this time delay in the operation of the relay can be varied within certain limits as may be desired.

In case it is desired to deenergize the load I2 it is only necessary to depress the normally closed push button 49, this push button thereby serving to interrupt both the relay closing coil circuit and the normally closed circuit. The coils then actoppositely to neutralize the holding flux so that the relay I1 is immediately operated to its open circuit position to deenergize the operating coil of the contactor H.

In the form of my invention shown in Fig. 4, the relay I1 is provided with two operating coils 60 and GI, the coil 60 being provided with more turns than the coil 6|. Both coils are energized to close the relay II, the coils 6| being energized to maintain the relay in its closed circuit position, the other coil 60 being connected in 9. normally closed circuit to delay the decay of magnetic fiux in the same manner as described in the forms or my invention described above. In the operation of this form of my invention the normally open start button 83 is momentarily depressed to complete an energizing circuit for the relay l1 which may be traced from the supply line I0, by conductor 84, normally closed interlock contacts of the contactor l4, conductors 66 and 51, start push button 83, conductors 68 and 5,5, normally closed contacts 10 of a stop push button 1|, conductor 12, coils and 5| of the relay l1, conductor 14, rectifier l5, and by conductor 11 to the other supply line H. The relay [1 is thereupon operated to its attracted position against the bias oi! the opening spring 2! to complete through its contacts 19 an energizcontrolling the enersization oi coil for said relay. a rectifier,

ing circuit for the operating coil of the contactor l4. Consequent to the closing or the contactor H the normally closed interlocks 85 are .operated to their open. circuit position to include the holding resistor .58 in circuit with the relay II, the holding circuit being completed through a pair of contacts ll closed by the armature oi the relay II. This circuit may be traced from the supply line In, by conductor 64, holding resistor 58, conductors 68 and I8, interlock contacts ll, conductor I1, relay contacts Ill, relay'coil 6| conductors I4 and I5, rectifier l6, and by conductor 11 to the other supply line I I. The ,coil 60 at the same time is short-circuited by the closing oi the contacts III operated with the relay II. This circuit may be traced from one side of the coil ill, by conductor It, contacts 10, conductors 69 and I1, relay contacts 80 and to the other side 01' the coil 80.

In order to deenergize instantaneously the con tactor l4, itis only necessary to press the stop button II to open the normally closed contacts Ill and to close momentarily its normally open contacts 03. The closing or the contacts 83 en-v ergizes the coil 60 in a direction to oppose the energizationor the coil 6|. This circuitmay be traced from the supply line I 0, by conductor 64, holding resistor 58, conductors 86 and", contacts Ii, conductor 01, relay contacts ll, relay coil ll, conductor 12, contacts 03, conductor 15, rectifier 16, and by conductor 11 to the other supply line H. Since the coil 0 is provided with more turns than the coil I, it will be apparent that the magnetic fiux holding the armature oi the relay l'| in the closed circuit position will lmmediatelybe reduced to zero, thereby causing the instant opening of the holding circuit of the contactor l4.

' While I have shown particular embodiments of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope 01' my invention.

What I claim as new and desire to secure b Letters Patent 0! the United States is:

1. An undervoltage protective system for an alternating current device, comprising a relay prow vided with'a magnetizable frame and a magnetizable armature normally biased from an attracted to anunattracted positionyan operating connecting means for connecting said coil and said rectifier in series inanenergizing clrcuitior operating said armature to its attracted position, and connecting means also providing a normally closed circuit for said coil for maintaining said armature in said attracted position a predetermined time after the said armature from one to the other oi said positions tor'controlling the energization'oi said alternating current device.

2. A time delay undervoltage protective system, comprising a contactor for controlling the energization oi-an alternating current device, a normally open relay provided with a substantially closed magnetic circuit and an'operating coil tor means including a rectifier .101 I relay with direct current, said rectifier providing a closed circuit for said relay so as-to delay the said contactor, energizing saidopening of said relay in case its energization is decreased a predetermined amount, and means Ior-interrupting said closed circuit for instantly opening said relay.

3. An undervoltage protective system for an alternating current device, comprising a relay provided with a magnetizable frame and a magnetizable armature biased from an attracted position to an unattracted position, said armature when in said attracted position forming in conjunction-with said frame a substantially closed magnetic circuit, an operating coil for said re- 1am a full wave rectifier of the bridge type, connecting means for connecting said relay coil across said rectifier, said connecting means including a normally closed circuit interrupter and connecting means for connecting said rectifier to said alternating current source, a contactor provided with an operating coil for controlling the energization of said alternating current device, means for momentarily energizing said contactor operating coil to close said contactor, means responsive to the closing of said contactor for completing said alternating current energizing circuit for said rectifier whereby said relay coil operates said armature from its unattracted to its attracted position, and means responsive to said operation of said relay for completing a holding circuit for said contactor operating coil, said rectifier permitting the flow of current in said relay coil in case of a predetermined reduction in the voltage of said alternating current source whereby said relay armature is maintained in its attracted position a time interval after said reduction in voltage.

4. An undervoltage protective system for an alternating current device, comprising a relay provided with a magnetizable frame and a magnetizable armature normally biased irom ran attracted position. to an unattracted position, said armature when in said attractedposition forming in conjunction with said frame a substantially closed magnetic circuit, a plurality of operating coils for saidrelay, an energizing circuit including a rectifier for one of said coils, connecting means including a normally closed push button for connecting another of said coils in a closed circuit for delaying the operation of said armature from said attracted to said unattracted 1 position inthe event oi a decrease in the voltage applied to said energizing circuit, said normally closed push button permitting the instant'opening of said relay.

' 5. An undervoltage protective system for an alternating current device, comprising a contactor for controlling the'energization of said device, said contactor being provided with a contactor operating coil and interlock contacts, a relay provided with a magnetizable frame and a magnetizable armature, normally biased from an attracted position to an unattracted position, said armature when in said attracted position forming cluding a normally closed circuit interrupter, a

normally open circuit interrupter for completing an energizing circuit through said normally closed circuit interrupter for at least one 01'- said relay 1 operating-coils to operate said armatureztosaid attractedposition, and means operative by said armature to energize said contactor operating coil, whereby the opening of said normally closed circuit interrupter interrupts said energizing circuit and said normally closed circuit to permit the instant operation of said magnetizable armature to said unattracted position.

6. An undervoltage protective system for an alternating current device, comprising a relay provided with a magnetizable frame and a magnetizable armature normally biased from an attracted position to an unattracted position, said armature when in said attracted position forming in conjunction with said frame a substantially closed magnetic circuit, a pair of operating coils for said relay, a rectifier, a normally closed and a normally open circuit interrupter, connecting means for connecting said circuit interrupters in series circuit relation with one of said coils, the closing of said normally open circuit interrupter completing an energizing circuit for said relay, connections for connecting the other of said coils in a normally closed circuit including said normally closed circuit interrupter for delaying the operation of said armature from its attracted to its unattracted position in case of a predetermined decrease in the energization of said other coil, a contactor, operating means for said contactor energized in response to the operation of said armature from one to the other of its positions, said contactor controlling the energization of said alternating current device, and means responsive to the operation of said contactor for including said holding resistor in circuit with said one coil and for completing a holding circuit for said one coil including said normally closed circuit interrupter.

"I.A.n undervoltage protective system for an alternating current device, comprising a relay provided with a magnetizable frame and a magnetizable armature normally biased from an attracted position to an unattracted position and when in said attracted position forming in conjunction with said frame a substantially closed magnetic circuit, a pair of operating coils for said relay, connecting means including a normally open and a normally closed circuit interrupter for energizing both of said coils to operate said relay, a contactor provided with an operating means controlled by said relay, said contactor controlling the energization of said alternating current device, and means responsive to the .operation of said contactor for connecting one of said coils in a normally closed circuit and for completing a holding circuit for the other of said coils.

8. An undervoltage protective system for an alternating current device, comprising a relay provided with a magnetizable frame and a magnetizable armature normally biased from an attracted position to an unattracted position and when in said attracted position forming in conjunction with said frame a substantially closed magnetic circuit, a pair of operating coils for said relay, connecting means including a normally open and a normally closed circuit interrupter connected in series for energizing both of said coils to operate said relay armature to its attracted position, a load controlling contactor controlled by said relay for controlling the energization of said alternating current device, means responsive to the operation of said contactor for connecting one of said coils in a normally closed circuit and for completing a holding circuit for the other of said coils, and means for instantly deenergizing said relay including an energizing circuit completed by the operation of one of said circuit interrupters for energizing one of said coils in opposition to the other thereby to decrease quickly the holding effort of said relay.

9. An undervoltage protective system for an alternating current device, comprising a relay provided with a magnetizable frame and a magnetizable armature normally biased from an attracted to an unattracted position and when in said attracted position forming in conjunction with said frame a substantially closed magnetic circuit, an operating coil for said relay, connect ing means for connecting said relay coil in a closed circuit, a rectifier for supplying direct current to said coil, a contactor operable to a closed circuit position for energizing said alternating current device, operating means responsive to said relay for maintaining said contactor in said closed circuit position when said relay is in said attracted position, and means responsive to the operation of said contactor to an open circuit position for interrupting the energization of said relay coil, said normally closed circuit of said relay coil and said closed magnetic circuit maintaining said relay armature in said attracted position for a predetermined time interval.

10. An undervoltage protective system, comprising a load controlling contactor of the type which will operate from a closed to an open circuit position in case its energization is decreased a predetermined amount, a relay provided with an operating coil, a magnetizable frame and a magnetizable armature normally biased from an attracted position to an unattracted position and when in said attracted position forming in conjunction with said frame a substantially closed magnetic circuit, an energizing circuit for said relay coil, means operable by said armature when in said attracted position for completing a holding circuit for said contactor, and means responsive to the operation of said contactor to said open circuit position for interrupting said relay energizing circuit, and connections forming a closed circuit with said relay coil for delaying the decay of the flux in said magnetic circuit for a predetermined time interval.

11. An undervoltage protective system, comprising an alternating current contactor provided with an operating coil, said contactor being operable from a closed to an open circuit position in case of a predetermined reduction in the energization of said coil, a relay provided with an operating coil, a magnetizable frame and a magnetizable armature normally biased from an attracted to an unattracted position, a holding circuit for said contactor coil completed by opera tion of said armature to said attracted position, means operative by the operation of said contactor to said closed position for energizing said relay coil with direct current, connections completing a closed circuit for said relay coil whereby said holding circuit is maintained by said armature a predetermined time interval after said contactor operates to said open circuit position.

12. An undervoltage protective system, comprising a load controlling contactor provided with an operating coil, an alternating current energizing circuit therefor, a magnetic timing relay provided with an operating coil, a magnetizable frame and an armature arranged so that in its attracted position it completes a holding circuit for said contactor operating coil, a rectifier for supplying direct current to said relay coil, connections forming a closed circuit for said relay coil to delay for a predetermined time interval the operation of said armature from said attracted to an unattracted position, said contactor being operable from a closed to an open circuit position in response to a predetermined reduction in the energizatlon of its operating coil, and means responsive to said operation of said contactor for initiating timing of said relay whereby said contactor can be operated to its closed circuit position in the event its energize.- tion is substantially increased before the expiration of said time interval.

13. An undervoltage protective system, comprising an electrical device operable between predetermined positions. an energizing circuit for said device for maintaining it in any of its positions so long as its energization is above a predeposition whereby said termlned value, a relay provided with at least one operating coil, a magnetizable frame and a magnetizable armature normally biased from an attracted to an unattracted position, a holding circuit for said electrical device completed by said armature when in its attracted position, means for energizing said relay, means responsive to the operation of said electrical device when its energization is decreased below said predetermined value i'or deenerg 'ng said relay, and means for completing a closed circuit for one relay coil when said armature is in its attracted armature is maintained in said attracted position a predetermined time interval after it is deenergized.

BENJAMIN W. JONES. 

